This application claims priority under 35 USC xc2xa7119 to, and the benefit of, UK Patent Application No. 0204515.1 filed Feb. 26, 2002.
The present invention relates to form-fill-seal machines, which traditionally come as either horizontal form-fill-seal machines (HFFS) or vertical form-fill-seal (VFFS) machines. Although the present invention is exemplified in terms of a tube-forming unit for a horizontal form-fill-seal machine, the invention may equally be applied to a vertical form-fill-seal machine using ultrasonic sealing of the overlapping margins of the film along a longitudinal line to define the tube into which the product articles are to be inserted.
Traditionally, the longitudinal seal in an HFFS machine has been achieved using a heat seal apparatus which contacts the outer surface of the superposed film margins to define a lap seal to finish a tube which can then be sealed transversely to separate one pack from the next, there being a product placed inside the tube between successive transverse seals as the first such seal is formed but before the second such seal is formed, and so on through the packaging process.
The longitudinal lap seal can be achieved using an ultrasonic sealing unit which traditionally involves an emitter of ultrasonic vibrations (sonotrode or hammer) and an anvil such that the films to be sealed are compressed between the hammer and the anvil and become sealed as a result of the transmission of energy thereto resulting from the ultrasonic vibrations of the hammer.
In the case of an HFFS machine, one side of the lap seal can be inside the tube and the other side can be outside the tube. An anvil can be mounted on the film forming box so as to be positioned inside the film tube while the sonotrode or hammer is mounted on the outside of the tube.
In the present invention, the anvil can be mount entirely independently of the forming box, but preferably integral with the mount for the sonotrode or hammer, such that the gap between the sonotrode and the anvil is not going to vary with any machine vibrations arising in use of the HFFS machine.
In one aspect of the invention, a tube-forming unit for a form-fill-seal machine comprises a form-fill-seal forming box, an ultrasonic vibration emitter, and an anvil able to be positioned such that film portions to be longitudinally lap sealed can pass between the anvil and the ultrasonic vibration emitter; characterised in that the anvil is mounted on an anvil carrier independent of the form-fill-seal forming box, to isolate the anvil from any vibrations sustained by the forming box.
In a second aspect of the invention, an ultrasonic sealing unit for the longitudinal lap sealing of a film conformed into a tubular form comprises an anvil secured, through an anvil carrier, to the underside of a carrier body which also supports a sonotrode vertically positioned over and in register with the anvil, wherein the anvil carrier comprises a first anvil support portion arranged to extend transversely across the machine direction, and a second anvil support portion, integral with the first anvil support portion, but defining therewith a gap through which a lower longitudinal edge of the film can pass over said second anvil support portion, thus becoming available for lap sealing to an upper longitudinal edge of the film.